Annular pulley system

A belt driven linear actuator comprising:

• a support structure;
• an output shaft;
• a first pulley system comprising:
• a first plurality of sheaves coupled to the support structure;
• a second plurality of sheaves coupled to the output shaft;
• and
• a flat belt extending between and around the first plurality of sheaves and the second plurality of sheaves with a predetermined number of free spans between them, and out of the first pulley system, wherein the first pulley system is configured such that removing belt from the first pulley system causes the second plurality of sheaves to translate the output shaft along an axis of travel in a contracting direction;
• a second pulley system comprising:
• a third plurality of sheaves arranged in an annular configuration and coupled to the support structure, wherein the third plurality of sheaves at least partially surround the output shaft;
• a fourth plurality of sheaves arranged in an annular configuration and coupled to the output shaft, wherein the fourth plurality of sheaves at least partially surround the output shaft;
• the flat belt extending between and around the third plurality of sheaves and the fourth plurality of sheaves with the predetermined number of free spans between them, wherein the second pulley system is configured such that removing belt from the second pulley system causes the fourth plurality of sheaves to translate the output shaft along the axis of travel in an expanding direction;
• and
• a belt drive mechanism configured to transfer belt between the first pulley system and the second pulley system.